In semiconductor and display industries, pattern forming technologies are classified into 3 categories. One is a subtractive method mainly applied to thin film technologies wherein a functional layer is deposited on a substrate, a photo-resist layer is patterned by lithography on the functional layer, and then the functional layer is etched into a pattern. Another is an additive method of contact printing such as screen-printing used primarily in thick film technologies. The other is a subtractive-additive method adopting both of a subtractive method and an additive method.
The formation of an electrically conductive pattern used for a display usually employs an additive method, which includes a step for forming a continuous pattern with an appropriate ink or paste by a contact or a non-contact printing method and a step for post-treatment to fix it on a substrate. In some cases, a subtractive/additive process further comprising a step of etching may be employed.
A number of studies to ink for forming a pattern by using an MOD material have been made ever since Vest, R.W. tested inks made of MOD material (IEEE Transactions on Components, Hybrids and Manufacturing Technology, 12(4), 545-549, 1987).
Herein, MOD (metallo-organic decomposition) material means an organic metal compound, which is decomposed and metallized at a temperature lower than the melting point of a metal.
U.S. Pat. No. 6,878,184 (issued to Kovio, Inc.) disclosed a technology for ink having nanoparticles formed from an MOD and a reducing agent (for example, aldehyde). However, this technology requires a stringent reaction condition, and a large amount of expensive MOD material. Further, the formed nanoparticles cannot provide sufficient electrical conductivity.
The advantage of MOD inks and inks made of suspended nanoparticles has relatively low metallization temperatures. However, they are disadvantageous in that they require high cost, and the electrical conductivity is remarkably reduced, as compared with that of a bulk metal.
International Patent Publication WO98-37133 (issued to Kydd, et al.) suggested a composite composition consisting of a MOD material and a particulate metal for screen printing ink by combining high electrical conductivity of a bulk metal and lower metallization temperature of MOD material. However, this patent does not disclose a printing ink of which the metallization temperature is low enough to be applied on a plastic substrate. Further, since the MOD material and the particulate metal are in the form of particles, further steps for finely pulverizing them with a vehicle by a ball mill are required to prepare the ink. The ink prepared by the above method has poor adaptability to various occasions, and should be used as a manufacturer prescribes.